Indiana University Health Proton Therapy Center
Chee-Wai Cheng, Ph.D.
Machine configuration and layout
Fixed beam line, double scattering and propeller
Gantry roomUniform scanning nozzle and snout
Rangemodulator
Indiana University Health Proton Therapy Center
• 3 snout sizes (10cm, 20cm and 30cm)• 30-40 patients treated per day• Typical patient mix (present time): prostate
(30%), H&N (30%), Peds+brain (40%)
Indiana University Health Proton Therapy Center
• Current Clinical Staffing
– 6 physicists and 2 medical physics assistants– 8 therapists and 3 therapist assistants– 3 dosimetrists– 5 radiation oncologists (4 treat patients between the PTC
and the IU Cancer Center).
Daily Machine QA• MPA/Physicist performs the QA:
– Alignment • Lasers, snout, x-rays and DR panels, gantry, light-field
– Safety• X ray systems, barcode scanner, intercom, cameras, panic button,
patient positioner, floor panels, interlocks
– Beam• Output constancy, flatness and symmetry, radiation survey (Friday
only)
• Typically takes 30 minutes per room• Therapist check room readiness
– Patient positioner, gantry, snout, DDS, BDS
Daily QA
Monthly QA (gantry room)• Output factor for the reference condition in water
phantom with calibrated IC and Elect.
• Range and SOBP (2.8, 10, 14.5cm) for 10cm field-size for three energy ranges: low, medium and high using a MLIC
• Symmetry and flatness at the middle of 10cm SOBP for the 3 snout sizes (10, 20 and 30cm) and the three energy ranges (low, medium and high) with MatrixX
• Typically takes 4-5 hours per room
SOBP measurement with MLIC
0
20
40
60
80
100
8 10 12 14 16 18 20 22 24
DD
Prox Bound
Dist Bound
Annual QA• Additional QA (not performed in monthly):
– Gantry isocentricity with star-shot– Linearity of OF-MU, OF-Cvolt, OF constancy-dose rate, – OF vs gantry angle– All three snout alignment at full extension/retraction– Snout position check at 270o and 90o at full
extension/retraction for all three snouts.– X-ray source tests:
• kVp calibration, exposure reproducibility, timer accuracy, mAs linearity, HVL
• Dosimetry protocol: TRS398– ADCL calibrated Advanced Markus chamber and
electrometer.
Mechanical Isocenter Checkwith pointer and x-rays
Light and Rad coincidence
Star shot
Patient Support System
• Degree of freedom:(x, y, z), Pitch, roll, Yaw
• Motion accuracy• Reproducibility• Adoptability• Compatibility • Safety
Treatment Table & Robotic systems QA
Dose monitor linearity
TR3 Ion Chamber Charge vs. DDS Requested MU(Constant Dose Rate)
y = 0.0067x - 0.0401R2 = 0.9992
y = 0.0193x + 0.001R2 = 1
0 100 200 300 400 500 600 700
MarkusA12/10Linear (Markus)Linear (A12/10)
DDS requested MU
0.01.02.03.04.05.06.07.08.09.0
10.011.012.0
Elec
trom
eter
Cha
rge
(nC)
OF variation with gantry angle
0.98
0.99
1.00
1.01
1.02
0 20 40 60 80 100
120
140
160
180
200
220
240
260
280
300
320
340
360
Gantry Angle
Dos
e V
aria
tion
TR2
TR3
Patient Specific QA• Relative output factor measurements in water
phantom of aperture and compensator for each field– For field size<3cm diameter, measurements taken
at different points along SOBP to locate appropriate point of measurement (MLIC was used before).
• QA tolerances– Relative output factor ±2% for both open (aperture only)
and closed (with compensator)• Re-measure to confirm discrepancy • Move IC along SOBP to examine change in OF to understand the
discrepancy
Unique Implementations at IUHPTC
• Quarterly QA– Absolute cross-calibration of all IC available (4)– Laser alignment– Robot alignment, constancy– 10cm snout alignment at full retraction/extension w/ x rays
and four cardinal gantry angles– X ray and DR panel alignment using x rays– Light and radiation coincidence– Emergency stop and emergency power in wall outlet
Top 3 items in our wish list (if we could have them in the future)
• Commercial Imaging system for Image Guidance (eg., MedCom, kVCT, In-room CT)
• Spot scanning
• Record-and-verify system
• Chris Allgower• Mark Wolanski• Li Zhao• Leia Fanelli• Archana Gautam• Len Coutinho• Brian Allen• Ryan Reed• Indra Das• Laddie Derenchuk• IUCO Engineering staff• IUCO software engineers
Acknowledgement
http://www.google.com/search?q=analemma&rls=com.microsoft:en-us:IE-SearchBox&tbm=isch&tbo=u&source=univ&sa=X&ei=XwT8UeSgBYycrQHPi4CoCw&ved=0CEIQsAQ&biw=888&bih=820